The treemap layout can now be set to "sticky" mode, which preserves the row
arrangements from an earlier layout. This is particularly handy for animating
treemaps, as it avoids the temporary occlusion as nodes swap positions. Thanks
to @philogb and the New York Times for the inspiration!

This fixes a bug with the usage of `require` in env-js, such that env-js now
uses proper relative paths rather than unshifting "." onto `require.paths`. The
behavior of `require` is documented here:
<http://nodejs.org/docs/v0.4.2/api/modules.html#all_Together...>
With this change in place, it's now possible to use env-js simply by require'ing
it from a script, rather than having env-js host and eval.
Also, this commit changes the initialization of env-js, such that the initial
document is immediately available when the env-js module is loaded. And, the
event loop is disabled so that env-js shuts down cleanly. This probably breaks
some parts of env-js, but it makes it much easier to use so I'm going to play
with it a bit.